Ask three suppliers to quote a screw press for your plant and the prices can differ by a factor of two — for what looks like the same machine. The usual explanation is that one supplier is expensive and another is cheap. The more common explanation is that the three suppliers were not quoting the same job at all, because they were given different sludge data, or none.
A screw press is not bought the way a pump is bought. There is no single “standard” machine that fits every sludge. The model, the size, the polymer dosing unit and the price all follow from four numbers about your sludge. Send those numbers first and every quotation you receive will be for the same machine, priced on the same basis. Skip them, and you will spend weeks comparing quotations that cannot be compared.
Why the Supplier Asks About Sludge, Not About the Press
The first thing to understand is that a screw press is sized on dry-solids load — the weight of dry solids that must pass through the machine per hour — not on the size of your plant or the size of the press you think you need. Two plants with the same daily wastewater flow can produce very different sludge loads. One produces a small volume of thick sludge; the other produces a large volume of thin sludge. The press each one needs is different, and so is the price.
That is why a serious supplier answers a request for a quotation with questions about your sludge before talking about models. HNS’s volute screw press range runs from the HL101 to the HL404, and which model fits your plant is decided by your sludge numbers, not by the catalogue. A supplier who quotes a model without asking for those numbers is guessing. A supplier who asks for them is doing the job properly — and the quotation you get back will be one you can hold them to.
The same discipline applies on the media side: our MBBR quotation guide starts from five numbers for exactly the same reason. A quotation without data is a guess with a price attached.
The 4 Numbers That Decide Your Quotation
1. Sludge type and source
What is the sludge, and where does it come from? Municipal waste activated sludge, industrial biological sludge, DAF float, digested sludge and chemical sludge all behave differently in a press. DAF float, for example, is oily and light and conditions differently from a municipal sludge of the same solids content. An industrial sludge may carry fibres, grit or oil that affect wear and screening.
Send the source process in one line — “municipal WWTP, waste activated sludge after secondary clarifier” tells a supplier far more than “sludge from our plant”. If the sludge comes from more than one stream, say so, and say whether they are mixed before dewatering or dewatered separately. A press quoted for one stream and fed a mixture is a press quoted for the wrong job.
2. Daily sludge volume
How many cubic metres of sludge per day need dewatering? Give the figure as it is, not as an average that hides the peaks. If the volume varies by day of the week or by production shift, say so — a press that copes with the average day and chokes on the peak day is undersized, and you will find out on the busiest day of the week.
Volume alone does not size the machine, but volume without solids content is meaningless, and solids content without volume is equally meaningless. The two numbers together are what the supplier needs. Send both, every time.
3. Inlet solids content
What percentage of your sludge is dry solids as it arrives at the press? This is the number buyers most often leave out, usually because nobody has measured it recently. It matters more than almost anything else: the same 10 m³ per day at 1% solids and at 3% solids is three times the dry-solids load, and that can be the difference between two models.
If you have a recent laboratory result, send it with the date. If you only have a typical range, send the range and say it is a range. If you have no measurement at all, say so honestly — a supplier would rather know the number is missing than build a quotation on a figure you guessed. What you must not do is send a round number you invented because the form asked for one. A guessed solids content produces a precisely wrong quotation.
4. Operating hours per day
How many hours a day will the press run? The same daily sludge load spread over 8 hours needs a machine roughly three times the hourly capacity of one spread over 24 hours. Operating hours are therefore a sizing input, not a footnote — and they are also a cost input, because a smaller machine running longer is usually cheaper to buy than a larger machine running a short shift, while the labour and energy balance points the other way.
Send the hours you actually plan to run, and whether the press will run continuously or in batches. If your plant runs the press only when an operator is present, say so. The supplier can then size the machine for your real working pattern instead of an assumed 24-hour day.
| Number | What to send | Why it decides the price |
|---|---|---|
| Sludge type and source | Process and stream, e.g. municipal WAS, DAF float, industrial biological | Conditioning, wear, screening — the machine configuration |
| Daily volume | m³/day, with peaks noted | Throughput the press must handle |
| Inlet solids content | % dry solids, dated lab result if available | With volume, gives dry-solids load — the sizing basis |
| Operating hours | Hours/day, continuous or batch | Hourly capacity needed, and the size-versus-running-cost balance |
Send anything else you have as well — current polymer type and dose if the sludge is already conditioned, the discharge route for the cake, and the space available for the machine. But the four numbers above are the minimum. A quotation built on them can be compared with another quotation built on them. A quotation built on fewer is not comparable with anything.
What a Comparable Quotation Must Contain
Once the suppliers have the same data, the quotations should be judged on the same points. Check that each one states the model, the scope of supply, and what is excluded. Does the price include the polymer preparation and dosing unit, or is that a separate item? Does it include the control panel, the discharge conveyor, spare wearing parts and commissioning support? Is freight included, and on which basis — EXW, FOB or CIF? Our freight guide for media explains those terms, and the same logic applies to equipment: two quotations at the same price are not the same price if one is EXW and the other is CIF.
If you are still deciding between dewatering technologies, read our screw press versus filter press comparison first — it sets out the practical differences before you spend time on quotations for the wrong machine. And if the technical side of sizing interests you, the sizing method itself — how dry-solids load becomes a model size — is covered on our technical site, Hydronovus. That is the calculation behind the quotation; the quotation itself is the commercial document, and it belongs here.
The Missing-Data Trap
Three things go wrong when the four numbers are missing. First, the supplier sizes on a guess and the machine arrives too small — the most expensive outcome, because it cannot be fixed with a phone call. Second, the supplier sizes generously to cover the unknown, and you pay for capacity you will never use. Third, and most common, each supplier guesses differently, so the quotations cannot be compared at all and the decision is made on price alone — which rewards the supplier who guessed smallest.
All three are avoidable. A day spent measuring your sludge — one volume reading, one solids test, one honest note about operating hours — is worth more than a week spent negotiating quotations that were built on different assumptions.
What to Send HNS for a Screw Press Quotation
Send us the four numbers: sludge type and source, daily volume in m³/day, inlet solids content in percent, and planned operating hours per day. Add your location and destination port, the polymer you use now if any, and any space or height limit in the dewatering room. We will reply with the model from the HL101–HL404 range that fits your dry-solids load, what is included in the price, and the freight and payment terms — so you can compare our quotation against any other on the same basis.
See the volute screw press range for the equipment, and then contact us with your four numbers. A quotation that starts from your sludge is a quotation you can trust; one that starts from a catalogue page is not.
